1. Field of the Invention
The present invention relates to apparatus for the positioning of a photosensitive material to present successive image areas to receive light images and also for other operations, and particularly to electronic circuit controlled apparatus for transporting photosensitive material in discrete steps and in mutually perpendicular directions so as to locate successive image areas for recording of images therein, in frame-by-frame sequence along the columns (or across the width of the photosensitive material before cutting).
The invention is especially suitable for use in computer output microfilmers (COM) for the control of film handling and cutting operations therein. The invention is generally applicable for use in film handling apparatus for moving the film with a high degree of accuracy.
2. Description of the Prior Art
In prior computer output microfilmers, means are provided for recording complete pages in small regions of a film. Each region may be considered to be a frame. The frames are so small that a large number of frames may be recorded across the width of a film. A length of film having such frames in an X-Y pattern of rows extending lengthwise of the film and columns extending across the film is called fiche or microfiche.
In order that the requisite pattern of frames and length of the fiche be obtained it is necessary to transport the film with a high degree of accuracy. Each frame must be located precisely in a film gate where it can be scanned by the image producing apparatus such as described in the above referenced Spaulding application. Inasmuch as any film transport mechanism presents a load having inertia, it is oftentimes difficult to obtain accurate film positioning.
Stepping motors have often been used when accurate and repeatable positioning of a load is desired (see for example U.S. Pat. Nos. 2,686,282; 3,444,447; 3,463,985; 3,523,230; 3,582,752; and 3,671,826). Such motors alone do not afford sufficient control to accurately move film in mutually perpendicular directions for the recording of frames of graphical information in columns across the film and in rows along the length of the film. The transient responses to the passage of current pulses through the windings of such stepping motors may cause dynamic positioning errors due to inertial effect of the transport mechanism resulting in misregistration of the frames in the film gate. It is conventional, as shown in the above-referenced patents and particularly U.S. Pat. No. 3,523,230, to apply pulses to switch current through the windings of stepping motors so as to make the motor step programmed distances in programmed directions. Nevertheless, the dynamic errors may cause a motor to be out of synchronism with the pulses and be displaced from the position corresponding to the pulse sequence. Halting the pulse sequence when the load reaches a reference point maintains the error between the actual load position and the position corresponding to the pulse sequence which has brought the load to the reference position.
Upon completion of the exposure of a certain length of film, it is sometimes desirable to cut the film thereby forming fiche which are then processed. It has been suggested that a solenoid actuated cutting mechanism be used for cutting various webs upon command; the command signal causing the discharge of a capacitor through a solenoid operating winding for energizing the solenoid and bringing the mechanism to cutting position (see U.S. Pat. No. 3,684,373).